Blends of curable epoxy resins with various thermoplastic polymers are known. For example, compositions comprising epoxy and polyester thermoplastic resins have been used as hot melt adhesives and in the manufacture of structural bonding and sealing tapes.
Latently curable compositions consisting of epoxy resins and thermoplastic polyesters have several deficiencies. For example, they can be prone to excessive flow prior to or during cure, unless flow control additives are incorporated. This excessive flow may result in a messy adhesive bond line that must be smoothed out in a subsequent step in cases where appearance is important (for example, exterior automotive applications such as trim adhesion, body panel, and door skin replacement) or it may lead to unevenness in thickness of the bond line (that is, seal) or to perforation (that is, blow-through) of the film by entrapped bubbles which may then be a source for water leaks. Further, in order to obtain good adhesion to painted metal substrates, it is often necessary to increase the epoxy content of the sealant composition above that level which otherwise achieves optimal properties. Also, epoxy-polyester sealant compositions known in the art having adequate flow properties typically lack sufficient tack to be used in the form of a thermosettable pressure-sensitive adhesive tape without a separate adhesive layer.
Epoxy material containing compositions having thermal catalysts or hardeners are typically difficult to melt process into articles (for example, tapes, films, or rods) without causing premature curing of the composition. Use of high temperature curatives that do not cause curing during such processing steps can cause excessive flow of the adhesive during cure, thereby resulting in defective bond or damage to the substrate to which it is to be bonded.
Other epoxy resin/thermoplastic resin blends provide films having inadequate tack or adhesion to vertical metal surfaces. One solution to this problem is to incorporate magnetic particles into the composition so to effect magnetic adhesion to the metal surface. The particles are added to the composition and then, in a separate step, are magnetized before the adhesive is used. However, this solution would not be effective for adhesion to polymer based substrates and adds expense and additional steps to the manufacturing process of adhesives for use on ferromagnetic substrates.